Method for removing gas film formed during electrodeposition



United States Patent 3,441,489 METHOD FOR REMOVING GAS FILM FORMED DURING ELECTRODEPOSITION Gerald R. Gacesa, Tarentum, Pa., assignnr to PPG Industries, Inc., a corporation of Pennsylvania No Drawing. Filed Oct. 22, 1965, Ser. No. 502,433 Int. Cl. C23b 1 3/ 00; B01k 5/00 US. Cl. 204-181 Claims ABSTRACT OF THE DISCLOSURE The method involves removal of the electrode from the bath after electrodeposition has been commenced and then the electrode is reinserted into the bath. Preferably the electrode is rinsed or means are employed to disrupt the occluded gas film while such electrode is out of the bath.

This invention relates to a method of electrodepositing a coating on a conductive base. More particularly, this invention relates to a method of increasing the film build of the coating on an article applied by electrodeposition by renewing the surface being coated during the electrodeposition process.

Electrodeposition is a relatively new coating technique which, although based on well-known principles, has only recently become technically feasible through the development of electrodepositable compositions which have the desired characteristics to meet the demands placed on a modern coating material The coatings achieved have excellent properties for many applications and electrodeposition results in a coating which does not run or wash off during baking. Virtually any conductive substrate may be coated by electrodeposition. The most commonly employed substrates include the base metals such as iron, steel, aluminum, copper, zinc, brass, tin, nickel and chromium, as well as other metals and pretreated metals, impregnated paper or other substrates rendered conductive under the conditions employed may also be coated.

While electrodeposition is in many respects advantageous compared to ordinary application methods, problems have arisen in the fact that for any given system at any given voltage there is a practical limitation as to the amount of film that can be built upon the substrate being coated and if the voltage is increased above a certain point, which varies with the system, the rupture voltage, i.e., that voltage at which the paint film ruptures and the amperage remains relatively constant or increases, is exceeded.

It has now been found that if the article being coated is withdrawn from the electrodeposition bath after electrodeposition has been commenced and then reinserted that a significantly greater film build can be achieved before the rupture voltage is exceeded.

At least one theory advanced for this result is that, since electrodeposition is conducted in an aqueous media, during the electrodeposition at least some electrolysis occurs and gases are produced at the electrodes and that these gas bubbles are occluded to the article being coated, which serves as one of the eletrodes. This layer of gas bubbles then interferes with the desired mechanisms which produce film build on the electrode.

It has now been found that by simply removing the article from the electrodeposition bath, and thus apparently disrupting this occluded gas film, and then continuing the electrodeposition process that greater film can be achieved. While some improvement is noted by merely removing the article being coated, preferably some means is employed to speed or assure the removal of the undesired coating on the surface. Such methods include im purging a stream of air or other gas upon the surface of the article to aid in disrupting or removing any occluded material or vibrating the article being coated to achieve the same effect. Still another method comprises rinsing the surface with the electrodepositable composition contained in the bath. The preferred method, however, is to rinse the article being coated with water. The reason why washing with water achieves results which are significantly greatly than merely withdrawing the article being coated are not totally clear. It is thought, however, that in addition to providing greater mechanical force, the water also removes additional contaminants such as soluble ions, and the like, which may interfere with the desired electrodeposition mechanisms.

A number of electrodepositable resins are known and can be employed to provide the electrodepositable composition of this invention. Virtually any water soluble, waterdispersible or water-emulsifiable polycarboxylic resinous material can be electrodeposited and, if film-forming, provides a coating which may be suitable for certain purposes. Any such electrodepositable is included among those which can be employed in the present invention, even though the coating obtained may not be entirely satisfactory for certain specialized uses.

The preferred resins which may be employed in the process invention comprises a reaction product or adduct of the drying oil or semi-drying oil fatty acid ester with a dicarboxylic acid or anhydride. By drying oil or semidrying oil fatty acid esters are meant esters of fatty acids which are or can be derived from drying oils or semidrying oils, or from such sources as tall oil. Such fatty acids are characterized by containing at least a portion of polyunsaturated fatty acids. Preferably, the drying oil or semi-drying oil per se is employed. Generally, drying oils are those oils which have an iodine value of above about 130, and the semi-drying oils are those which have an iodine value of about to 130, as determined by method ASTMDl46757T. Examples of such esters include linseed oil, soya oil, safflower oil, perilla oil, tung oil, oiticica oil, poppyseed oil, sunflower oil, tall oil esters, walnut oil, dehydrated castor oil, herring oil, menhaden oil, sardine oil, and the like.

Also included among such esters are those in which the esters themselves are modified with other acids, including saturated, unsaturated or aromatic acids such as butyric acid, stearic acid, lineoleic acid, phthalic acid, isophthalic acid, therphthalic acid or benzoic acid, or an anhydride of such an acid. One inexpensive acid material which has been found to produce good results in many instances is rosin, which is composed of chiefly abiotic acid and other resin acids. The acid modified esters are made by transesterification of the ester, as by forming a dior m'onoglyceride by alcoholysis, followed by esterification with the acid; they may also be obtained by reacting oil acids with a polyol and reacting the acid with the partial ester. In addition to glycerol, alcoholysis can be carried out using other polyols such as trimethylolpropane, pentaerythritol, sorbitol and the like. If desired, the esters can also be modified with monomers such as cyclopentadiene or styrene and the modified esters produced thereby can be utilized herein. Similarly, other esters of unsaturated fatty acids, for example, those pre pared by the esterification of tall oil fatty acids with polyols, are also useful.

Also included within the terms drying oil fatty acid esters and semi-drying oil fatty acid esters as set forth herein are alkyd resins prepared utilizing semi-drying or drying oils; esters of epoxides with such fatty acids, including esters of diglycidyl ethers of polyhydric compounds as well as other mono-, diand polyepoxides; semi-drying or drying oil fatty acid esters of polyols, such as butanediol, trimethylolethane, trimethylolpropane, trimethylolhexane, pentaerythritol, and the like; and semidrying or drying fatty acid esters of resinous polyols such as homopolymers or copolymers of unsaturated aliphatic alcohols, e.g., allyl alcohol or methallyl alcohol, including copolymers of such alcohols with styrene or other ethylenically unsaturated monomers or with non-oil modified alkyl resins containing free hydroxyl groups.

Any alpha, beta-ethylenically unsaturated dicarboxylic acid or anhydride can be employed to produce the reaction products described herein. These include such anhydrides as maleic anhydride, itaconic anhydride, and other similar anhydrides. Instead of the anhydride, there may also be use ethylenically unsaturated dicarboxylic acids which form anhydrides, for example, maleic acid or itaconic acid. These acids appear to function by first forming the anhydride. Fumaric acid, which does not form an anhydride, may also be utilized, although in many instances it requires more stringent conditions than the unsaturated dicarboxylic acid anhydrides or acids which form such anhydrides. Mixtures of any of the above acids or anhydrides may also be utilized. Generally speaking, the anhydride or acid employed contains from 4 to 12 carbon atoms, although longer chain compounds can be used if so desired.

While the exact nature of the reaction product of the acid or anhydride with the fatty acid ester is not known with certainty, it is believed that the reaction takes place by addition of the unsaturated linkage of the acid or anhydride to the carbon chain of the oil. In the case of nonconjugated double bonds, such as are present in linseed oil, the reaction may take place with the methylene group adjacent to the non-conjugated double bond. In the case of oils having conjugated double bonds, such as tung oil, the reaction is probably of the Diels-Alder type.

The reaction between the acid or acid anhydride and the drying oil or semi-drying oil fatty acid ester takes place readily without the use of a catalyst and at temperatures in the range of about 100 C. to about 300 C. or higher, with the reaction generally being carried out between about 200 C. and about 250 C.

While the reaction products can be compromised solely of adducts of the fatty acid ester and the dicarboxylic acid or anhydride, in many instances it is desirable to incorporate into the reaction product another ethylenically unsaturated monomer. The use of such monomer often produces films and coatings which are harder and more resistant to abrasion and which may have other similar desirable characteristics. For this purpose, any ethylenically unsaturated monomer can be employed. Examples of such monomers include monoolefinic and diolefinic hydrocarbons such as styrene, alpha-methyl styrene, alphabutyl styrene, vinyl toluene, butadiene-l,3, isoprene, and the like; halogenated monoolefinic and diolefinic hydrocarbons, such as alpha-chlorostyrene, alpha-bromostyrene, chlorobutadiene and similar compounds; esters of organic and inorganic acids, such as vinyl acetate, vinyl propionate, vinyl 2-chlorobenzoate, methyl acrylate, ethyl methacrylate, butyl methacrylate, heptyl acrylate, decyl methacrylate, methyl crotonate, isopropenyl acetate, vinyl alpha-bromopropionate, vinyl alpha-chlorovalerate, allyl chloride, allyl cyanide, allyl bromide, allyl acetate, dimethyl itaconate, dibutyl itaconate, ethyl alpha-chloroacrylate, isopropyl alpha-bromoacrylate, decyl alpha-chloroacrylate, dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, and diethyl glutaconate; organic nitriles, such as acrylonitrile, methacrylonitrile, and ethacrylonitrile; and the like.

As is apparent from the above discussion and the ex- .4 amples set forth, which, of course, do not include all of the ethylenically unsaturated monomers which may be employed, any such monomer can be utilized. The preferred class of monomers can be described by the formula:

where R and R are hydrogen or alkyl, R; is hydrogen, alkyl or carboxyalkyl and R is cyano, aryl, alkyl, alkenyl, aralkyl, alkaryl, alkoxycarbonyl or aryloxycarbonal. The preferred compounds are styrene, substituted styrenes, alkyl acrylates, alkyl methacrylates, dioolefins and acrylonitrile.

The reaction of the fatty acid ester, the acid or anhydride and any additional monomer or monomers can be carried out concurrently, that is, with each of the com ponents of the reaction product being mixed together and heated to reaction temperature. However, because the monomer and the acid or anhydride are often quite reactive with each other, the oil or other fatty acid ester is preferably first reacted with the acid or acid anhydride, and then this product is subsequently reacted with any ehtylenically unsaturated monomer or monomers employed. For example, a reaction product of linseed oil, maleic anhydride and styrene is made by first reacting maleic anhydride with linseed oil and then reacting the maleinized oil with styrene. When the process is carried out in this manner, the reaction of the additional monomer with the initial reaction product is usually carried out at somewhat lower temperatures, usually bet-ween about 25 C. and 200 C.

The proportions of each of the components going to make up the reaction product are ordinarily not critical.

Generally speaking, between about 10 percent and about 45 percent by weight of the unsaturated acid or acid anhydride is reacted with from about 55 percent to about 9.0 percent by weight of fatty acid ester. In the presently preferred products, usually 15 percent to 3 0 percent of anhydride and 70 percent to percent of oil ester are employed. If an ethylenically unsaturated monomer is incorporated in the reaction product, it is typically used in amounts between about 5 percent and about 35 percent by Weight, based upon the total weight of acid or anhydride and ester, with between 10 percent and 25 percent being used in those products preferred at present. Thus, in most instances the total composition of the reaction product may comprise from about 35 precent to about percent by weight of the fatty acid ester and from about 10 percent to about 65 percent of the acid or anhydride and other monomer combined, with between about 6 percent and about 45 percent of the acid or anhydride always present.

The products produced in the above manner are comprised of polymeric chains of moderate length. The average molecular weight of the products to be used in electrodeposition should be low enough so that its flow characteristics at high solids are maintained, but high enough to provide adequate throwing power. The desirable molecular weight levels vary with the coating composition and conditions employed. Generally those products having molecular weights of up to 10,000 or somewhat higher have given the best results.

Neutralization of these products is accomplished by reaction of all or part of the dicarboxylic anhydride groups with a base. Usually up to about half of such groups are neutralized in unesterified adducts; the partially esterified products are often neutralized to a greater extent, based on unesterified acid groups remaining.

It is preferred in certain instances that the neutralization reaction be carried out in such a manner that amido groups are attached to part of the carbonyl carbon atoms derived from the dicarboxylic acid or hydride. By amido groups are meant trivalent nitrogen atoms attached with one valence to the carbonyl carbon atom with the other two valences being linked to hydrogen or carbon atoms in the same or different organic radicals. Amido groups are formed, for example, when the reaction with the neutralizing base is carried out with a water solution of ammonia, a primary amine or a secondary amine, or when the product is reacted with such an amine in the absence of water.

Compositions within this general class are described in copending applications, Ser. No. 222,674, filed Sept. 10, 1962, now US. 3,366,563 and Ser. No. 282,880, filed May 24, 1963, now US. 3,369,983.

Another type of electrodepositable coating composition which gives desirable results are the water-dispersible coating compositions comprising at least partially neutralized interpolymers of hydroxyalkyl esters of unsaturated carboxylic acids, unsaturated carboxylic acids and at least one other ethylenically unsaturated monomer. These are employed in the composition along with an amine-aldehyde condensation production or a polyepoxide, or both, with the interpolymer usually making from about 50 percent to about 95 percent by weight of the resinous composition.

The acid monomer of the interpolymer is usually acrylic acid or methacrylic acid, but other ethylenically unsaturated monocarboyxlic and dicarboxylic acids, such as ethacrylic acid, crotonic acid, maleic acid, or other acids of up to about 6 carbon atoms can also be employed. The hydroxyalkyl ester is usually hydroxyethyl or hydroxypropyl acrylate or methacrylate, but also desirable are the various hydroxyalkyl esters of the above acids having, for example, up to about 5 carbon atoms in the hydroxyalkyl radical. Monoor diesters of the dicarboxylic acids mentioned are included. Ordinarily, the acid and ester each comprise between about 1 percent and about 20 percent by Weight of the interpolymer, with the remainder being made up of one or more other copolymerizable ethylenically unsaturated monomers. The most often used are the alkyl acrylates, such as ethyl acrylate; the alkyl methacrylates, such as methyl methacrylate; and the vinyl aromatic hydrocarbons, such as styrene; but others can be utilized.

The above interpolymer is at least partially neutralized by reaction with a base as described above; at least about 10 percent, and preferably 50 percent or more of the acidic groups are neutralized, and this can be carried out either before or after the incorporation of the interpolymer in the coating composition. The bases above can be used, with ammonia and amines being preferred; except when a polyepoxide is present, in which case there is preferably employed a hydroxide, such as sodium hydroxide, or if an amine, a tertiary amine.

The amine-aldehyde condensation products included in these compositions are, for example, condensation products of melamine, benzoquanamine, or urea with formaldehyde, although other amine-containing amines and amides, including triazines, diazines, triazoles, guanadines, guanamines and alkyl and aryl-substituted derivatives of such compounds can be employed, as can other aldehydes, such as acetaldehyde. The alkylol groups of the products can be etherified by reaction with an alcohol, and the products utilized can be water-soluble or organic solvent-soluble.

The electrodepositable compositions can also include a polyepoxide, which can be any epoxide compound or mixture with an epoxy functionality of greater than 1.0. Numerous such polyepoxides are known and are described in patents such as US. Patents Nos. 2,467,171; 2,615,007; 2,716,123; 2,786,067; 3,030,336; 3,053,855; and 3,075,999. Included are polyglycidyl ethers of polyphenols, such as bisphenol A, or of aliphatic polyhydric alcohols, such as 1,4-butanediol; polyglycidyl esters of polycarboxylie acids, such as diglycidyl adipate; and polyepoxides from the epoxidation of unsaturated alicyclic compounds, such as 3,4-epoxy-6-methylcyclohexylmethyl 3,4 epoxy 6 methylcyclohexanecarboxylate.

Electrodeposition compositions comprising the above interpolymers and an amine-aldehyde resin or a polyepoxide, or both, are more fully described in copending application Ser. No. 368,394, filed May 18, 1964.

Still another electrodepositable composition of desirable properties comprises an alkyd-amine vehicle, that is, a vehicle containing an alkyd resin and an amine-aldehyde resin. A number of these are known in the art and may be employed. Preferred are water-dispersible alkyds such as those in which a conventional alkyd (such as a glyceryl phthalate resin), which may be modified with drying oil fatty acids, is made with a high acid number (e.g., 50 to 70) and solubilized with ammonia or an amine, or those in which a surface active agent, such as a polyalkylene glycol (e.g., Carbowax), is incorporated. High acid number alkyds are also made by employing a tricarboxylic acid, such as trimellitic acid or anhydride, along with a polyol in making the alkyd.

The above alkyds are combined with an amine-aldehyde resin, such as those described hereinabove. =Preferred are water-soluble condensation products of melamine or a similar triazine with formaldehyde with subsequent reaction with an alkanol. An example of such a product is hexakis(methoxymethyl) melamine.

The alkyd-amine compositions are dispersed in water and they ordinarily contain from about 10 percent to about 50 percent by weight of amine resin based on the total resinous components.

Examples of compositions of this class are described in US. Patents Nos. 2,852,475; 2,852,476; and 2,853,459.

The neutralization and solubilization of the above vehicles is accomplished by the use of a base. Inorganic bases such as metal hydroxides or, more desirably, antmonia can be used for this purpose, as can organic bases, particularly amines. Among the preferred class of neutralizing bases are ammonia and any basic amine. Examples of such amine are primary and secondary amines including alkyl amines, such as methylamine, ethylamine, propylamine, butylamine, amylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, and N-methylbutylamine; cycloalkyl amines, such as cyclohexylamine; unsaturated amines, such as allylamine, 1,2-dimethyl-pentenylamine and pyrrole; aryl amines, such as aniline; aralkyl amines such as benzylamine and phenethylamine; alkaryl amines, such as m-toluidine; cyclic amines, such as morpholine, pyrrolidine and piperidine; diamines, such as hydrazine, methylhydrazine, 2,3-toluenediamine, ethylenediamine, 1,2-naphthalenediamine and piperazine; and substituted amines, such as histamine, hydroxylamine, ethanolamine, and diethanolamine, as well as tertiary amines.

It has been found advantageous in many instances to effect part of the neutralization with certain solid amines, notably amino-alkyl-alkanediols, such as, for example, 2-methyl-2-amino 1,3 propanediol, 2-ethyl-2- amino-1,3-propanediol or Z-methyI-Z-amino-1,4-b-utanediol. The films produced when a small amount of such amines are employed are considerably harder and often have improved water resistance. However, preferably not more than about 4 percent by weight of the resinous components of these solid amines are utilized, since they are relatively expensive and greater amounts do not further improve the films properties and may even slightly decrease its water resistance.

The electrodepositable coating compositions of the instant invention comprise the above vehicles, containing a strontium chromate-containing pigment composition. The pigment composition, in addition to strontium chromate, may be of any conventional type, comprising, for example, iron oxides, lead oxides, carbon black, titanium dioxide, talc, barium sulfate and the like, as well as combinations of these and similar pigments. Color pigments such as cadmium yellow, cadmium red, phthalocyanine blue, chromic yellow, toluidine red, hydrated iron oxide and the like may be included if desired. Better results with pigmented compositions are attained if the weight ratio of pigment solids to vehicle solids is not higher than about 1.5 to 1, and preferably not higher than about 1 to 1.

There may also be included in the coating composition, if desired, additives such as antioxidants, for example, orthoamyl phenol or cresol (the commercial mixture of isomeric cresols is satisfactory). It is found especially advantageous to include such antioxidants in coating compositions which are used in baths which may be exposed to atmospheric oxygen at elevated temperatures and with violent agitation over extended periods of time.

In formulating the coating composition, ordinary tap water may be employed. However, such Water may contain a relatively high level of metals and cations; while not rendering the process inoperative, the use of water containing these cations may result in variations in the properties of the bath when used for electrodeposition. Thus, it is often desirable to utilize deionized water, i.e., water from which free ions have been removed as by passage through an ion exchange resin, in making up the coating compositions of the invention.

Other additives which may be included in the coating composition if desired include, for example, wetting agents such as petroleum sulfonates, sulfated fatty amides, esters of sodium isothionates, or alkylphenoxypolyoxyethylene alkanols, as well as driers such as the linoleates, the naphthenatcs, the octanates and the tallates of such metals as lead, cobalt, manganese, iron, copper and zirconium. Other additives which may be employed include antifoaming agents, suspending agents, bactericides and the like.

In electrodeposition processes employing the various coating compositions described above, an aqueous bath containing the coating composition is placed in contact with an electrically conductive anode and an electrically conductive cathode. The surface to be coated is employed as one of the electrodes. In the specific examples of compositions described above, the surface to be coated is employed as the anode. Upon the passage of electric current between the anode and the cathode, while in contact with the bath containing the coating composition, an adherent film of the coating composition is deposited. The conditions under which the electrodeposition step herein is carried out are those conventionally used in electrodeposition of coatings. The applied voltage may be varied greatly and can be, for example, as low as 1 volt or as high as several thousand volts, although typically between 50 volts and 500 volts. The current density is usually between about 0.1 ampere and 15 amperes per square foot, and is high initially and tends to decrease during the electrodeposition of a single article.

The concentration of the non-volatile components (i.e., vehicle and any pigments and the like) in the aqueous bath is not critical and relatively high levels can be employed. However, it is ordinarily desirable to use as loW a concentration as gives satisfactory results, and in the cases of the above-described compositions, aqueous compositions containing as little as 1 percent by Weight of non-volatile solids can be employed, while those containing between 5 percent and 20 percent by weight are preferred.

EXAMPLE I Parts by weight Deionized water 23.40 Diethylamine 1.50

The above were mixed and then there was added:

Parts by weight Resin A (above) 14.40

Mixing was continued for 10 minutes and there was added:

Parts by weight Cresylic acid 0.22

Diethylamine 0.79

After an additional period of 10 minutes the pH was adjusted to 10.0. There was then added:

Parts by weight Dlspersmg agent (combination oil soluble sulfonate non-ionic surfactant-Witco 912) 0.53 Basic lead silico chromate 40.00 Red iron oxide 11.85 Deionized water 7.30

The above final mixture was mixed for 10 minutes and then run through a continuous attritor to attain a maximum grind of 6 /2 Hegman reading.

The electrodeposition primer was made up as follows:

Parts by weight (grams) Resin A (above) 228.3 Pent-oxone (4-methoxy-4-methyl-pentanone-2) 18.0 Cresylic acid 3.4

The above were mixed and were added to 15.9 parts of diethylamine dissolved in 134.0 parts deionized water and then the entire mixture was agitated. There was then added:

Parts by weight Deionized water 314.8

After a thorough mixing there was added:

Parts by weight Paste B (above) 200.0

The pH of the above mixture was approximately 8.

The above primer was then diluted with deionized water to bring the solids content of the mixture to 8 percent. The 8 percent solids material was used in the following experiment.

Phosphate treated steel panels (Bonderite 37) were coated as follows:

TABLE I Film Tune Temperature thickness Voltage (Seconds) (Degrees F.) Amps (mils) Appearance 280 86 1. 5-. 25 1191A "{Water wash 280- 90 86 .35-.19 0.5 Good 280 90 S7 1. 5. 25 and B "{Water wash 400 90 81 .5-.24 "'ifi Good 280 90 87 1. 5-. 25 Panelo {Remained in bath 400..... 90 87 Ruptured Ruptured EXAMPLE 11 This example shows coating two dissimilar electro-depositable coatings.

A vehicle resin (Resin G) was prepared as follows. The following were charged into a reactor:

Parts by weight Linseed oil 700.0 Pentaerythn'tol 8 8.0 Trimethylolethane 100.0

The above mixture was heated to 190 C. and 0.24 parts litharge was added to the reaction. The reaction mixture was then heated to about 240250 C. and held for one hour at that temperature. The mixture was cooled to 190 C. and the following added:

Parts by weight Phthalic anhydride 444.0 Dimethylolpropionic acid 137.0

Parts by weight Deionized water 317.4

Diglycol amine [2-(2-aminoethoxy)ethanol] 12.0 Resin G (above) 176.4

was added, with stirring:

Cresylic acid 1.5 Deionized water 100.2

The above mixture had a pH of 6.55 and was designated Solubilized Resin H.

A pigment paste (Paste I) was prepared by charging the following into a steel canister containing steel balls:

Parts by weight Deionized water 292.0 Dispersing agent (a nonylphenolpoly(ethyleneoxy) phosphate ester-GAFAC PE510) 11.25

Stir and add:

Barium sulfate 340.0 Strontium chromate 20.0 Carbon black (Raven Black 15) 40.0

Parts by weight Coconut fatty acids 726 Neopentyl glycol 1272 were charged into a reactor equipped with water condenser and trap, thermometer and inert gas line. The mixture was heated to 182 C. and held to an acid number of 25. There was then added:

Parts by weight Adipic acid 225.0 Trimellitic acid 1008.0

The mixture was then heated to l82187 C. and held to an acid number of 50-55 and 750 parts of tertiary butanol was added and the resin cooled.

A total of 268 grams of water was recovered from the trap.

A solubilized vehicle resin based on the above resin was prepared as follows. To a mixture of:

Parts by weight Deionized water 380.0 Triethylamine 33.3

was added:

Resin L (above) 422.0

The pH of the mixture was adjusted to 7.2 with triethylamine. This is designated as Resin L Solubilized.

A pigment paste (Paste M) was prepared as follows. The following mixture was prepared:

Parts by weight Resin L Solubilized (above) 332.5 Deionized water 137.2 Triethylamine 4.8

Dispersing agent (combination oil-soluble sulfonate and non-ionic surfactantWitco 912) 9.5 Titanium dioxide 957.0

Resin L Solubilized (above) 228.0 Hexakis (methoxymethyl) melamine (melted at F. before addition) 102.5 Paste M (above) 134.0

The above was let down to 8 percent solids at a pH of 7.8 with deionized water.

A zinc phosphate treated steel panel (Bonderite 37) was coated as follows:

First the panel was coated with the black primer composition at 84 F. at volts for 60 seconds (1.3- .35 amperes). The panel was removed from the bath, washed with water and placed in the white topcoat bath and coated at 200 volts for 90 seconds. The total film build was 2.3 mils, which is higher than the normal uniform film build of either of the two compositions.

When the base coat has been partially cured, such as by baking for short periods, it has been found that the second coat can still be applied although the film build is not as great. If the first coat is fully cured, little or no deposition of the second coat is obtained.

I claim:

1. In a method of electrodepositing an electrodepositable composition from an electrodeposition bath comprising a solubilized polycarboxylic acid resin on an electrode surface, the improvement comprising removing the electrode from the bath after coating of the electrode has commenced and subsequently reinserting the electrode into an electrodeposition bath comprising a solubilized polycarboxylic acid resin and continuing the coating of said electrode.

2. A method as in claim 1 where the electrode is washed with water prior to reinserting the electrode into an electrodeposition bath.

3. In a method of electrodepositing an electrodepositable composition from an electrodeposition bath comprising a solubilized polycarboxylic acid resin on an electrode surface, the improvement comprising removing the electrode from said electrodeposition bath after coating of the electrode has commenced, employing means to disrupt the occluded film upon said coating and subsequently reinserting the electrode into an electrodeposition bath comprising a solubilized polycarboxylic acid resin and continuing to coat said electrode.

4. A method as in claim 3 Where the electrode is reinserted into an electrodeposition bath of substantially the same composition as the original electrodeposition bath.

5. A method as in claim 3 Where the electrode is reinserted into an electrodeposition bath comprising a solubilized polycarboxylic acid resin, said bath having a composition dissimilar to the original electrodeposition bath.

6. In a method of electrodepositing an electrodepositable composition from an electrodeposition bath cmpris ing a solubilized reaction product of a drying oil fatty acid ester with a member of the group consisting of alpha, beta-ethylenically unsaturated dicarboxylic acids on an electrode surface, the improvement comprising removing the electrode from the bath after coating of the electrode has commenced and subsequently reinserting the electrode into an electrodeposition bath comprising a solubilized polycarboxylic acid resin and continuing the coating of said electrode.

7. A method as in claim 6 Where the electrode is Washed with water prior to reinserting the electrode into an electrodeposition bath.

8. In a method of electrodepositing an electrodepositable composition from an electrodeposition bath comprising a solubilized reaction product of a drying oil fatty acid ester with a member of the group consisting of alpha, beta-ethylenically unsaturated dicarboxylic acids on an electrode surface, the improvement comprising removing the electrode from the bath after coating of the electrode has commenced, employing means to disrupt the occluded film upon said coating and subsequently reinserting the electrode into an electrodeposi tion bath comprising a solubilized polycarboxylic acid resin and continuing to coat said electrode.

9. A method as in claim 8 where the electrode is reinserted into an electrodeposition bath of substantially the same composition as the original electrodeposition bath.

10. A method as in claim 8 where the electrode is reinserted into an electrodeposition bath comprising a solubilized polycarboxylic acid resin, said bath having a composition dissimilar to the original electrodeposition bath.

11. In a method of electrodepositing an electrodepositable composition from an electrodeposition bath comprising an alkyd resin on an electrode surface, the improvement comprising removing the electrode from the bath after coating of the electrode has commenced and subsequently reinserting the electrode into an electrodeposition bath comprising a solubilized polycarboxylic acid resin and continuing the coating of said electrode.

12. A method as in claim 11 where the electrode is Washed with Water prior to reinserting the electrode into an electrodeposition bath.

13. In a method of electrodepositing an electrodepositable composition from an electrodeposition bath comprising an alkyd resin on an electrode surface, the improvement comprising removing the electrode from the bath after coating of the electrode has commenced, employing means to disrupt occluded film upon said coating and subsequently reinserting the electrode into an electrodeposition bath comprising a solubilized polycarboxylic acid resin and continuing to coat said electrode.

14. A method as in claim 13 Where the electrode is reinserted into an electrodeposition bath of substantially the same composition as the original electrodeposition bath.

15. A method as in claim 13 where the electrode is reinserted into an electrodeposition bath comprising a solubilized polycarboxylic acid resin, said bath having a composition dissimilar to the original electrodeposition bath.

References Cited UNITED STATES PATENTS 3,200,058 8/1965 Ostel' 204-481 3,230,162 1/1966 Gilchrist 204-181 FOREIGN PATENTS 587,039 4/ 1947 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner.

E. ZAGARELLA, Assistant Examiner. 

